If 35.5 grams of calcium oxide react with excess water, how many grams of calcium hydroxide can be formed?
CaO + H2O - Ca(OH)2

Mass of Ca(OH)2= 46.916 g

Given

Reaction

CaO + H2O - Ca(OH)2

Required

mass of Ca(OH)2

Solution

Mol of CaO :

= mass : MW

= 35.5 g : 56 g/mol

= 0.634

From the equation , mol ratio CaO : Ca(OH)2 = 1 : 1, so mol Ca(OH)2 = 0.634

Mass Ca(OH)2 :

= mol x MW

= 0.634 x 74

= 46.916 g

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !